use editor::{Editor, EditorEvent, MBTextSummary, MultiBufferSnapshot};
use gpui::{App, Entity, FocusHandle, Focusable, Styled, Subscription, Task, WeakEntity};
use settings::{RegisterSetting, Settings};
use std::{fmt::Write, num::NonZeroU32, time::Duration};
use text::{Point, Selection};
use ui::{
    Button, ButtonCommon, Clickable, Context, FluentBuilder, IntoElement, LabelSize, ParentElement,
    Render, Tooltip, Window, div,
};
use util::paths::FILE_ROW_COLUMN_DELIMITER;
use workspace::{StatusBarSettings, StatusItemView, Workspace, item::ItemHandle};

#[derive(Copy, Clone, Debug, Default, PartialOrd, PartialEq)]
pub(crate) struct SelectionStats {
    pub lines: usize,
    pub characters: usize,
    pub selections: usize,
}

pub struct CursorPosition {
    position: Option<UserCaretPosition>,
    selected_count: SelectionStats,
    context: Option<FocusHandle>,
    workspace: WeakEntity<Workspace>,
    update_position: Task<()>,
    _observe_active_editor: Option<Subscription>,
}

/// A position in the editor, where user's caret is located at.
/// Lines are never zero as there is always at least one line in the editor.
/// Characters may start with zero as the caret may be at the beginning of a line, but all editors start counting characters from 1,
/// where "1" will mean "before the first character".
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct UserCaretPosition {
    pub line: NonZeroU32,
    pub character: NonZeroU32,
}

impl UserCaretPosition {
    pub(crate) fn at_selection_end(
        selection: &Selection<Point>,
        snapshot: &MultiBufferSnapshot,
    ) -> Self {
        let selection_end = selection.head();
        let (line, character) = if let Some((buffer_snapshot, point, _)) =
            snapshot.point_to_buffer_point(selection_end)
        {
            let line_start = Point::new(point.row, 0);

            let chars_to_last_position = buffer_snapshot
                .text_summary_for_range::<text::TextSummary, _>(line_start..point)
                .chars as u32;
            (line_start.row, chars_to_last_position)
        } else {
            let line_start = Point::new(selection_end.row, 0);

            let chars_to_last_position = snapshot
                .text_summary_for_range::<MBTextSummary, _>(line_start..selection_end)
                .chars as u32;
            (selection_end.row, chars_to_last_position)
        };

        Self {
            line: NonZeroU32::new(line + 1).expect("added 1"),
            character: NonZeroU32::new(character + 1).expect("added 1"),
        }
    }
}

impl CursorPosition {
    pub fn new(workspace: &Workspace) -> Self {
        Self {
            position: None,
            context: None,
            selected_count: Default::default(),
            workspace: workspace.weak_handle(),
            update_position: Task::ready(()),
            _observe_active_editor: None,
        }
    }

    fn update_position(
        &mut self,
        editor: &Entity<Editor>,
        debounce: Option<Duration>,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        let editor = editor.downgrade();
        self.update_position = cx.spawn_in(window, async move |cursor_position, cx| {
            let is_singleton = editor
                .update(cx, |editor, cx| editor.buffer().read(cx).is_singleton())
                .ok()
                .unwrap_or(true);

            if !is_singleton && let Some(debounce) = debounce {
                cx.background_executor().timer(debounce).await;
            }

            editor
                .update(cx, |editor, cx| {
                    cursor_position.update(cx, |cursor_position, cx| {
                        cursor_position.selected_count = SelectionStats::default();
                        cursor_position.selected_count.selections = editor.selections.count();
                        match editor.mode() {
                            editor::EditorMode::AutoHeight { .. }
                            | editor::EditorMode::SingleLine
                            | editor::EditorMode::Minimap { .. } => {
                                cursor_position.position = None;
                                cursor_position.context = None;
                            }
                            editor::EditorMode::Full { .. } => {
                                let mut last_selection = None::<Selection<Point>>;
                                let snapshot = editor.display_snapshot(cx);
                                if snapshot.buffer_snapshot().excerpts().count() > 0 {
                                    for selection in editor.selections.all_adjusted(&snapshot) {
                                        let selection_summary = snapshot
                                            .buffer_snapshot()
                                            .text_summary_for_range::<MBTextSummary, _>(
                                            selection.start..selection.end,
                                        );
                                        cursor_position.selected_count.characters +=
                                            selection_summary.chars;
                                        if selection.end != selection.start {
                                            cursor_position.selected_count.lines +=
                                                (selection.end.row - selection.start.row) as usize;
                                            if selection.end.column != 0 {
                                                cursor_position.selected_count.lines += 1;
                                            }
                                        }
                                        if last_selection.as_ref().is_none_or(|last_selection| {
                                            selection.id > last_selection.id
                                        }) {
                                            last_selection = Some(selection);
                                        }
                                    }
                                }
                                cursor_position.position = last_selection.map(|s| {
                                    UserCaretPosition::at_selection_end(
                                        &s,
                                        snapshot.buffer_snapshot(),
                                    )
                                });
                                cursor_position.context = Some(editor.focus_handle(cx));
                            }
                        }

                        cx.notify();
                    })
                })
                .ok()
                .transpose()
                .ok()
                .flatten();
        });
    }

    fn write_position(&self, text: &mut String, cx: &App) {
        if self.selected_count
            <= (SelectionStats {
                selections: 1,
                ..Default::default()
            })
        {
            // Do not write out anything if we have just one empty selection.
            return;
        }
        let SelectionStats {
            lines,
            characters,
            selections,
        } = self.selected_count;
        let format = LineIndicatorFormat::get(None, cx);
        let is_short_format = format == &LineIndicatorFormat::Short;
        let lines = (lines > 1).then_some((lines, "line"));
        let selections = (selections > 1).then_some((selections, "selection"));
        let characters = (characters > 0).then_some((characters, "character"));
        if (None, None, None) == (characters, selections, lines) {
            // Nothing to display.
            return;
        }
        write!(text, " (").unwrap();
        let mut wrote_once = false;
        for (count, name) in [selections, lines, characters].into_iter().flatten() {
            if wrote_once {
                write!(text, ", ").unwrap();
            }
            let name = if is_short_format { &name[..1] } else { name };
            let plural_suffix = if count > 1 && !is_short_format {
                "s"
            } else {
                ""
            };
            write!(text, "{count} {name}{plural_suffix}").unwrap();
            wrote_once = true;
        }
        text.push(')');
    }

    #[cfg(test)]
    pub(crate) fn selection_stats(&self) -> &SelectionStats {
        &self.selected_count
    }

    #[cfg(test)]
    pub(crate) fn position(&self) -> Option<UserCaretPosition> {
        self.position
    }
}

impl Render for CursorPosition {
    fn render(&mut self, _window: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
        if !StatusBarSettings::get_global(cx).cursor_position_button {
            return div().hidden();
        }

        div().when_some(self.position, |el, position| {
            let mut text = format!(
                "{}{FILE_ROW_COLUMN_DELIMITER}{}",
                position.line, position.character,
            );
            self.write_position(&mut text, cx);

            let context = self.context.clone();

            el.child(
                Button::new("go-to-line-column", text)
                    .label_size(LabelSize::Small)
                    .on_click(cx.listener(|this, _, window, cx| {
                        if let Some(workspace) = this.workspace.upgrade() {
                            workspace.update(cx, |workspace, cx| {
                                if let Some(editor) = workspace
                                    .active_item(cx)
                                    .and_then(|item| item.act_as::<Editor>(cx))
                                    && let Some((_, buffer, _)) = editor.read(cx).active_excerpt(cx)
                                {
                                    workspace.toggle_modal(window, cx, |window, cx| {
                                        crate::GoToLine::new(editor, buffer, window, cx)
                                    })
                                }
                            });
                        }
                    }))
                    .tooltip(move |_window, cx| match context.as_ref() {
                        Some(context) => Tooltip::for_action_in(
                            "Go to Line/Column",
                            &editor::actions::ToggleGoToLine,
                            context,
                            cx,
                        ),
                        None => Tooltip::for_action(
                            "Go to Line/Column",
                            &editor::actions::ToggleGoToLine,
                            cx,
                        ),
                    }),
            )
        })
    }
}

const UPDATE_DEBOUNCE: Duration = Duration::from_millis(50);

impl StatusItemView for CursorPosition {
    fn set_active_pane_item(
        &mut self,
        active_pane_item: Option<&dyn ItemHandle>,
        window: &mut Window,
        cx: &mut Context<Self>,
    ) {
        if let Some(editor) = active_pane_item.and_then(|item| item.act_as::<Editor>(cx)) {
            self._observe_active_editor = Some(cx.subscribe_in(
                &editor,
                window,
                |cursor_position, editor, event, window, cx| match event {
                    EditorEvent::SelectionsChanged { .. } => Self::update_position(
                        cursor_position,
                        editor,
                        Some(UPDATE_DEBOUNCE),
                        window,
                        cx,
                    ),
                    _ => {}
                },
            ));
            self.update_position(&editor, None, window, cx);
        } else {
            self.position = None;
            self._observe_active_editor = None;
        }

        cx.notify();
    }
}

#[derive(Clone, Copy, PartialEq, Eq, RegisterSetting)]
pub enum LineIndicatorFormat {
    Short,
    Long,
}

impl From<settings::LineIndicatorFormat> for LineIndicatorFormat {
    fn from(format: settings::LineIndicatorFormat) -> Self {
        match format {
            settings::LineIndicatorFormat::Short => LineIndicatorFormat::Short,
            settings::LineIndicatorFormat::Long => LineIndicatorFormat::Long,
        }
    }
}

impl Settings for LineIndicatorFormat {
    fn from_settings(content: &settings::SettingsContent) -> Self {
        content.line_indicator_format.unwrap().into()
    }
}
